49 CFR § 213.53 - Gage.
§ 213.53 Gage.
(a) Gage is measured between the heads of the rails at right-angles to the rails in a plane five-eighths of an inch below the top of the rail head.
(b) Gage shall be within the limits prescribed in the following table—
| Class of track | The gage must be at least— | But not more than— |
|---|---|---|
| Excepted track | N/A | 4′10
|
| Class 1 track | 4′8″ | 4′10″. |
| Class 2 and 3 track | 4′8″ | 4′9
|
| Class 4 and 5 track | 4′8″ | 4′9
|